An HDAC Inhibitor, Entinostat/MS-275, Partially Prevents Delayed Cranial Suture Closure in Heterozygous Runx2 Null Mice.

Cleidocranial dysplasia (CCD) is an autosomal dominant skeletal disorder caused by mutations in RUNX2, coding a key transcription factor of early osteogenesis. CCD patients suffer from developmental defects in cranial bones. Despite numerous investigations and clinical approaches, no therapeutic strategy has been suggested to prevent CCD. Here, we show that fetal administration of Entinostat/MS-275, a class I histone deacetylase (HDAC)-specific inhibitor, partially prevents delayed closure of cranial sutures in Runx2+/- mice strain of C57BL/6J by two mechanisms: 1) posttranslational acetylation of Runx2 protein, which stabilized the protein and activated its transcriptional activity; and 2) epigenetic regulation of Runx2 and other bone marker genes. Moreover, we show that MS-275 stimulates osteoblast proliferation effectively both in vivo and in vitro, suggesting that delayed skeletal development in CCD is closely related to the decreased number of progenitor cells as well as the delayed osteogenic differentiation. These findings provide the potential benefits of the therapeutic strategy using MS-275 to prevent CCD. © 2017 American Society for Bone and Mineral Research.

Tomografía computarizada fetal de baja dosis para diagnosticar displasias óseas / Low-dose computed tomography to diagnose fetal bone dysplasias

Presentamos un caso de displasia cleidocraneal diagnosticado en la semana 25 de gestación mediante tomografía computarizada (TC) de baja dosis fetal. La sospecha era de displasia ósea grave debido al percentil bajo en los huesos largos y la apariencia ecográfica de craneosinostosis. La TC no demostró alteraciones incompatibles con la vida. La dosis efectiva de la prueba fue de 5 mSv, dentro del rango recomendado para estas exploraciones. La TC de baja dosis fetal es una técnica emergente que permite estudiar estructuras óseas con precisión a partir del segundo trimestre de gestación. En España, es legalmente posible interrumpir el embarazo en caso de malformación grave del feto incluso si se sobrepasa la semana 22 de gestación. Por tanto, ante la sospecha de una displasia ósea grave, el radiólogo debe conocer las estrategias para disminuir la dosis manteniendo una calidad diagnóstica suficiente, y conocer las estructuras óseas que debe evaluar (AU)

We present a case of cleidocranial dysplasia diagnosed by low-dose fetal computed tomography (CT) in the 25th week of gestation. Severe bone dysplasia was suspected because of the fetus’ low percentile in long bones length and the appearance of craniosynostosis on sonography. CT found no abnormalities incompatible with life. The effective dose was 5 mSv, within the recommended range for this type of examination. Low-dose fetal CT is a new technique that makes precision study of the bony structures possible from the second trimester of pregnancy. In Spain, abortion is legal even after the 22nd week of gestation in cases of severe fetal malformations. Therefore, in cases in which severe bone dysplasia is suspected, radiologists must know the strategies for reducing the dose of radiation while maintaining sufficient diagnostic quality, and they must also know which bony structures to evaluate (AU)

Low-dose computed tomography to diagnose fetal bone dysplasias. / Tomografía computarizada fetal de baja dosis para diagnosticar displasias óseas.

We present a case of cleidocranial dysplasia diagnosed by low-dose fetal computed tomography (CT) in the 25th week of gestation. Severe bone dysplasia was suspected because of the fetus' low percentile in long bones length and the appearance of craniosynostosis on sonography. CT found no abnormalities incompatible with life. The effective dose was 5 mSv, within the recommended range for this type of examination. Low-dose fetal CT is a new technique that makes precision study of the bony structures possible from the second trimester of pregnancy. In Spain, abortion is legal even after the 22nd week of gestation in cases of severe fetal malformations. Therefore, in cases in which severe bone dysplasia is suspected, radiologists must know the strategies for reducing the dose of radiation while maintaining sufficient diagnostic quality, and they must also know which bony structures to evaluate.

Loss of Tbx1 induces bone phenotypes similar to cleidocranial dysplasia.

T-box transcription factor, TBX1, is the major candidate gene for 22q11.2 deletion syndrome (DiGeorge/ Velo-cardio-facial syndrome) characterized by facial defects, thymus hypoplasia, cardiovascular anomalies and cleft palates. Here, we report that the loss of Tbx1 in mouse (Tbx1(-/-)) results in skeletal abnormalities similar to those of cleidocranial dysplasia (CCD) in humans, which is an autosomal-dominant skeletal disease caused by mutations in RUNX2. Tbx1(-/-) mice display short stature, absence of hyoid bone, failed closure of fontanelle, bifid xiphoid process and hypoplasia of clavicle and zygomatic arch. A cell-type-specific deletion of Tbx1 in osteochondro-progenitor (Tbx1(OPKO)) or mesodermal (Tbx1(MKO)) lineage partially recapitulates the Tbx1(-/-) bone phenotypes. Although Tbx1 expression has not been previously reported in neural crest, inactivation of Tbx1 in the neural crest lineage (Tbx1(NCKO)) leads to an absence of the body of hyoid bone and postnatal lethality, indicating an unanticipated role of Tbx1 in neural crest development. Indeed, Tbx1 is expressed in the neural crest-derived hyoid bone primordium, in addition to mesoderm-derived osteochondral progenitors. Ablation of Tbx1 affected Runx2 expression in calvarial bones and overexpression of Tbx1 induced Runx2 expression in vitro. Taken together, our current studies reveal that Tbx1 is required for mesoderm- and neural crest-derived osteoblast differentiation and normal skeletal development. TBX1 mutation could lead to CCD-like bone phenotypes in human.

A Runx2 threshold for the cleidocranial dysplasia phenotype.

Cleidocranial dysplasia (CCD) in humans is an autosomal-dominant skeletal disease that results from mutations in the bone-specific transcription factor RUNX2 (CBFA1/AML3). However, distinct RUNX2 mutations in CCD do not correlate with the severity of the disease. Here we generated a new mouse model with a hypomorphic Runx2 mutant allele (Runx2(neo7)), in which only part of the transcript is processed to full-length (wild-type) Runx2 mRNA. Homozygous Runx2(neo7/neo7) mice express a reduced level of wild-type Runx2 mRNA (55-70%) and protein. This mouse model allowed us to establish the minimal requirement of functional Runx2 for normal bone development. Runx2(neo7/neo7) mice have grossly normal skeletons with no abnormalities observed in the growth plate, but do exhibit developmental defects in calvaria and clavicles that persist through post-natal growth. Clavicle defects are caused by disrupted endochondral bone formation during embryogenesis. These hypomorphic mice have altered calvarial bone volume, as observed by histology and microCT imaging, and decreased expression of osteoblast marker genes. The bone phenotype of the heterozygous mice, which have 79-84% of wild-type Runx2 mRNA, is normal. These results show there is a critical gene dosage requirement of functional Runx2 for the formation of intramembranous bone tissues during embryogenesis. A decrease to 70% of wild-type Runx2 levels results in the CCD syndrome, whereas levels >79% produce a normal skeleton. Our findings suggest that the range of bone phenotypes in CCD patients is attributable to quantitative reduction in the functional activity of RUNX2.

An echo-poor spine at 13 weeks: an early sign of cleidocranial dysplasia.

OBJECTIVE: Early prenatal diagnosis of cleidocranial dysplasia (CCD) in a case in which molecular genetic analysis of the RUNX2 gene was non-informative. METHODS: 2D ultrasound examination. RESULTS: At week 13+6, a 2D ultrasound examination revealed a fetus with severely delayed ossification of the vertebral spine. The clavicles were barely seen and the calvarial bones were significantly less ossified than expected for gestational age. The fetus had otherwise normal anatomy and biometry. Serial ultrasound examinations during pregnancy confirmed the diagnosis, but the manifestations became less distinct. The diagnosis was confirmed clinically at birth. CONCLUSION: This case illustrates an early easily recognizable pattern of severely delayed ossification of the vertebral spine, which is probably a characteristic of CCD.

Reflections upon the aetiology of congenital pseudarthrosis of the clavicle. With a note on cranio-cleido dysostosis.

The cause of pseudarthrosis of the clavicle is obscure. Right-sidedness is an almost constant feature. We have proposed that the lesion is sometimes due to pressure upon the developing clavicle by the subclavian artery which is normally at a higher level on the right side. This may be accentuated in the presence of cervical ribs or unduly elevated first ribs, both of which we have observed in association with pseudarthrosis. We have also noted pseudarthrosis on the left side in association with dextrocardia (when the relative positions of the subclavian arteries are reversed) and in the presence of a large left cervical rib. We have speculated upon the nature of the clavicular defect in cranio-cleido dysostosis, in which disorder the first ribs are habitually elevated. A similar mechanism may be involved.